An anaerobic spirochete, Treponema hyodysenteriae, has been characterized as the primary etiological agent in swine dysentery. Harris, D. L.; Glock, R. D.; Christensen, C. R.; and Kinyon, J. M.: Vet. Med./Small Animal Clin. 67:61 (1972); Taylor, D. J.; and Alexander T. J. L.: Brit. Vet. J. 127:108 (1971). The pathogenesis of the disease has not been completely defined but there is evidence that T. hyodysenteriae proliferates in the large intestine of pigs in the presence of other secondary organisms and produces a mucohemorrhagic to necrotic enteritis. Meyer, R. C.; Simon, J.; and Byerly, C. S.: Vet. Pathol. 12:46 (1975). Local invasion of the epithelium and lamina propria has been observed but there is no apparent systemic invasion of the causative organism. Glock, R. D.; and Harris, D. L.: Vet. Med./Small Animal Clin. 67:65 (1972); Harris, D. L.; Glock R. D., Kinyon, J. M.: Intestinal Treponematoses. First Symposium on the Biology of Parasitic Spirochetes (1975). Little is known about the immunology of swine dysentery although resistance to reinfection can be demonstrated in convalescent pigs.
Because of the enteric nature of swine dysentery, it has been believed that effective immunization would involve localized immunity in the large intestine. Oral inoculation of attenuated or non-pathogenic isolates of T. hyodysenteriae have therefore been tested. However, results of such tests have been negative; no significant increase in the resistance of the swine to dysentery infection having been obtained. Hudson, M. J., Alexander, T. J. L., Lysons, R. J. and Wellstead, P. D.: Brit. Vet. J. (1974) 139:37.